A laboratory technician in Atlanta may have been exposed to the Ebola virus, reports the Centers for Disease Control and Prevention.

A small amount of material from an Ebola virus experiment that was transported Monday from one lab to another may have contained live virus. The material was on a sealed plate but should not have been moved into the second laboratory, the CDC said in a statement.

There was no exposure outside the secure laboratory and no exposure or risk to the public, the CDC says. The mistake was discovered by laboratory scientists Tuesday.

The lab technician who processed the material has no symptoms of the illness, the CDC says, and will be monitored for 21 days. Others who entered the lab will be assessed for possible exposure.

"We've made sweeping changes to our lab safety protocols over the last couple of months," said CDC spokesman Tom Skinner. "But these incidents that involve human error simply cannot happen and we'll get to the bottom of what happened here."

The incident involves a mixup in the color-coding of samples of Ebola being used in viability studies that were transferred from a biosafety level 4 lab, where scientists wear moonsuit-like protective gear and must take decontamination showers before leaving the pressurized facilities, to a biosafety level 2 lab, where staff typically wear only gowns and gloves. The technician who is being monitored for possible exposures worked in the biosafety level 2 lab, Skinner said.

The event is under internal investigation by the CDC and was reported to Secretary of Health and Human Services Sylvia Burwell. The CDC will provide a report on the event when the investigation concludes. The laboratory area had already been decontaminated and the material destroyed as a routine procedure before the error was identified. The laboratory was decontaminated for a second time and is now closed.

"I am troubled by this incident in our Ebola research laboratory in Atlanta," CDC Director Tom Frieden said in the statement. "We are monitoring the health of one technician who could possibly have been exposed and I have directed that there be a full review of every aspect of the incident and that CDC take all necessary measures."

This is the latest in a series of missteps by the CDC. Although the CDC is considered one of the world's premier public health agencies, the labs have been repeatedly cited in private government audits for failing to properly secure bioterror agents, according to restricted government watchdog reports obtained by USA TODAY earlier this year. CDC labs house some of the most deadly pathogens on the planet, including Ebola, SARS, monkeypox and dangerous strains of flu.

In July, the head of CDC's bioterrorism response lab resigned in the wake of his staff's mishandling of live anthrax spores and the potential exposure of dozens of agency employees to a particularly lethal strain of the bacteria. None were infected. Researchers had used an unapproved protocol to deactivate the spores, which were then transferred to a lower-level lab where workers have less protective equipment.

Earlier in the year, other CDC staff unwittingly cross-contaminated a relatively mild strain of bird flu with a dangerous strain that can kill people, then shipped it to another federal lab. The mistake was discovered in May when birds unexpectedly died in experiments at the U.S. Department of Agriculture lab. A CDC investigation concluded that sloppy lab practices by an experienced but overworked scientist rushing to get to a noon meeting was the likely cause of the error.

The incidents at CDC, plus the discovery of forgotten samples of deadly smallpox virus at a lab at the National Institutes of Health, prompted a congressional hearing last summer.